2-(3-Cyano-4-isobutyloxyphenyl)-4-methyl-5-thiazole carboxylic acid (hereinbelow sometimes referred to as Compound I) exhibits a potent xanthine oxidase inhibitory activity and an effect of decreasing uric acid in vivo and it has been marketed as a drug for the treatment of gout and an increased uric acid level. This Compound I is generally administered orally in the form of a tablet prepared by tabletting together with additives such as excipients; however, conventional tablets are immediate release tablets, with which the concentration of the drug rises in a short time, while maintenance of the concentration at a certain level or higher over a long period of time has been difficult. A sustained release preparation from which a drug is released gradually can be considered as one of the methods used when the blood concentration must be maintained at a certain level or higher over a long period of time.
A single-component matrix type sustained release preparation and a controlled release preparation using a coating film, a routine method, have been known as sustained release preparations and these preparations are expected to be able to maintain the blood concentration over a long period of time by releasing a drug gradually at a constant rate.
Further, preparations having a bimodal drug release profile to maintain and regulate the drug concentration in blood over a long period of time are also known, from which a drug is released rapidly when release starts and then gradually after a certain time, or on the contrary, a drug is released gradually when release starts and then rapidly after a certain time. A coat-core sustained release tablet is one of the dosage forms that enable such multiple-phase drug release.
Patent Literature 1 (Japanese Patent No. 2955524) describes a coat-core sustained release tablet of nifedipine, wherein an inner core (core portion) is an immediate release tablet and an outer layer portion is a sustained release matrix layer from which a drug is dissolved slowly so that a decrease in release rate due to a decrease in a volume is avoided.
Patent Literature 2 (Japanese Patent No. 3220373) describes a coat-core sustained release tablet of nifedipine with improved resistance to environment in the digestive tract having a strong mechanical stimulation, wherein an inner core (core portion) is a sustained release matrix tablet and an outer layer portion is a sustained release matrix containing a disintegration suppressing molecule from which a drug is dissolved slowly.
Patent Literature 3 (Japanese Patent No. 3751287) describes a small-sized coat-core sustained release tablet of nifedipine comprising a sustained release matrix from which a drug is dissolved slowly, wherein an inner core and an outer layer portion contain a disintegration suppressing molecule.
Patent Literature 4 (Japanese Patent No. 4637338) describes a solid coat-core preparation of cilostazol, wherein an inner core (core portion) is a sustained release matrix tablet from which a drug is dissolved rapidly and an outer layer portion is a sustained release matrix containing a water-insoluble substance from which a drug is dissolved slowly.
Patent Literature 5 (Japanese Patent Application Laid-open No. 2011-63611) describes a solid coat-core preparation of cilostazol, wherein an inner core (core portion) is a tablet containing a surfactant and an outer layer portion is a sustained release matrix from which a drug is dissolved slowly. This coat-core tablet is a preparation characterized by incorporating a surfactant in the inner core to improve the solubility of cilostazol and improve absorption of the drug from the regions ranging from the small intestine to the colon, the lower part of the digestive tract.